Problem: Simplify the following expression: $t = \dfrac{6}{7z} - \dfrac{2}{5z}$
Explanation: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $7z$ and $5z$ $\lcm(7z, 5z) = 35z$ $ t = \dfrac{5}{5} \cdot \dfrac{6}{7z} - \dfrac{7}{7} \cdot \dfrac{2}{5z} $ $t = \dfrac{30}{35z} - \dfrac{14}{35z}$ $t = \dfrac{30 -14}{35z}$ $t = \dfrac{16}{35z}$